1. Field of the Invention
The present invention relates to a radiation digital image photographing apparatus for photographing a radiation image by the use of a digital signal.
2. Related Background Art
Conventionally, an apparatus for obtaining a radiation image of an object by illuminating the object with radiation and detecting a distribution of the intensity of radiation transmitted through or penetrating the object has been widely used in the fields of medical diagnosis and non-destructive inspection for industry, etc. A film/screen method for radiation is known as a general method for effecting such photographing. This method is a method for effecting photographing under a condition in which a photosensitive film is combined with a fluorescent material sensitive to radiation. In this method, a sheet-shaped fluorescent member of rare-earth element capable of light emission upon its illumination with radiation is in close contact with and held on each of opposite surfaces of the photosensitive film, radiation transmitted through the object is converted into visible light by the fluorescent member, the light is captured by the photosensitive film, and a latent image formed on the film is developed by chemical treatment and visualized.
On the other hand, owing to recent advance of digital technology, use is made of a method in which after a radiation image is converted into an electrical signal and the electrical signal is image-processed, the thus-processed image is reproduced as a visible image on a CRT or the like, thereby obtaining a high-quality radiation image. In connection with such a method for converting the radiation image into the electrical signal, Japanese Patent Application Laid-Open Nos. H55-12429 and H56-11395, for example, disclose a radiation image recording and reproducing system in which after a radiation transmission image is once stored in a fluorescent member as a latent image, the fluorescent member is illuminated with stimulated light, such as laser light, to photoelectrically read the latent image, thereby outputting a visualized image of the radiation transmission image.
Further, as semiconductor process technology advances of late, there has been developed an apparatus for photographing a radiation image in a similar manner using a semiconductor sensor. Such a kind of system has a very wide dynamic range, and is capable of obtaining a radiation image that is unlikely to be influenced by fluctuation of the exposure amount of radiation, as compared with a conventional radiation photographing system which uses a photosensitive film. Further, no chemical treatment is needed, and an output image can be instantaneously obtained, differently from the conventional photosensitive film system.
Such a kind of photographing apparatus is generally settled and used in a radiation room, and its rigidity has been so far considered more important than the weight and size in a thickness direction of the radiation image photographing apparatus itself.
In recent years, however, a portable photographing apparatus, such as a so-called electronic cassette, is desired for the purposes of attaining speedy and wide-range photographing. Further, it is required in the light of advantages in the cost to establish a system in which a single photographing apparatus is mounted to a plurality of photographing supports at the same time to enable photographing of various portions.
In this case, it is desirable for operators, such as radiographic engineers, that the electronic cassette is light in weight, considering the operators' works in settling the electronic cassette at a predetermined location and transporting the electronic cassette. Further, if the size in the thickness direction of the electronic cassette is large, an object person is liable to be pained in the event that the electronic cassette is inserted into a spacing between the object person lying on a bed and the bed.
However, if the weight and thickness of the electronic cassette are reduced, a problem of reduction of its mechanical strength occurs. Furthermore, there is a possibility that some radiation penetrates the apparatus and goes outside, is then scattered by a wall, a floor and the like behind the apparatus, returns from behind the apparatus, and is finally input into a sensor in the apparatus. It is necessary to oppress such scattered radiation from behind the apparatus as much as possible, since such radiation can cause a difference in transmittance between parts of a structure in the photographing portion to be photographed in an image as a flare.
As discussed in the foregoing, a variety of appropriate measures have been desired to cope with enlarged thickness and increased weight of conventional radiation image photographing apparatuses.